Body Fat Calculator

The bathroom scale can't tell muscle from fat. Two people at the same weight and height can look and perform completely differently — one lean and athletic, the other carrying excess fat — and body fat percentage is the number that captures that difference. This calculator estimates your body fat percentage from simple measurements using three established methods, entirely in your browser.

What body fat percentage actually tells you

Body fat percentage is the share of your total body weight that is fat tissue, as opposed to muscle, bone, organs and water. It is a more useful health and fitness signal than weight alone, and often more useful than BMI, because BMI can misclassify muscular people as "overweight" and can miss excess fat in people who look slim. A rising body fat percentage — especially fat carried around the waist — is associated with higher cardiometabolic risk, which is why the waist measurement matters so much in the Navy method below.

The three methods, and how accurate each one is

No tape-measure or BMI-based method matches a DEXA scan or hydrostatic weighing. Each estimate below carries a typical error of roughly ±3–4 percentage points for most people, and more at the extremes. Use the result as a trend line to track over time, not as a clinical figure.

• Navy circumference method — developed by the U.S. Navy (Hodgdon & Beckett, 1984). It estimates fat from height, neck and waist (plus hip for women), so it needs only a tape measure. It is age-independent. Accuracy depends heavily on measuring at the right spots (see below); sloppy waist placement is the biggest source of error.
• BMI method (Deurenberg equation) — Deurenberg, Weststrate & Seidell (1991) derived body fat from BMI, age and sex. It needs no tape measure, but inherits BMI's core weakness: it can over-estimate fat for muscular builds and under-estimate it for older or sedentary people. Age genuinely changes the result, which is why this calculator now asks for it.
• Jackson–Pollock 3-site skinfold — Jackson & Pollock (1978, and Jackson, Pollock & Ward 1980 for women). With skinfold calipers you pinch three sites (chest/abdomen/thigh for men; triceps/suprailiac/thigh for women); the calculator converts the sum to body density and then to fat percentage. Done consistently by the same person, it is usually the most repeatable of the three — but it depends on good caliper technique and, like the BMI method, on your age.

Healthy body fat ranges

The colored bar under your result places you against the widely-cited American Council on Exercise (ACE) categories, which differ by sex because women carry more essential fat:

• Men — essential 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, above-average 25%+.
• Women — essential 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, above-average 32%+.

These are general reference ranges, not diagnostic thresholds. Athletic performance, age and genetics all shift what is healthy for an individual.

How to measure for the Navy method

• Neck — just below the larynx, tape sloping slightly down to the front; don't flex.
• Waist — for men, around the navel; for women, at the narrowest point. Relax; measure after a normal exhale, tape snug but not compressing.
• Hip (women) — around the widest part of the buttocks.
• Take each measurement twice and average them. A 2 cm error at the waist can shift the result by more than a full percentage point.

How to use this calculator

1. Choose your sex — the formulas differ for men and women.
2. Pick a method: Navy (tape measure), BMI (no measuring, needs your age) or Skinfold (needs calipers and your age).
3. Enter your measurements in centimeters (or millimeters for skinfolds). Results update live as you type.
4. Read your estimated body fat percentage, fat mass, lean mass and category. Re-check periodically under the same conditions to track the trend.

Frequently Asked Questions

Which method should I use?

If you only have a tape measure, use Navy — it's the most practical and doesn't need your age. If you have calipers and can measure consistently, Skinfold is usually the most repeatable. Use the BMI method only when you can't measure at all; it's the roughest of the three.

Why does the calculator ask for my age now?

The Deurenberg (BMI) and Jackson–Pollock (skinfold) equations are age-dependent — body fat at a given BMI or skinfold sum rises with age. An earlier version assumed age 30 for everyone, which skewed results for anyone younger or older; entering your real age fixes that. The Navy method doesn't use age, so the field is hidden for it.

How accurate is this compared with a DEXA scan?

DEXA and hydrostatic weighing are the reference standards; these field methods typically land within about 3–4 percentage points for most people. Treat the number as a good estimate and a consistent way to track change — not a lab result.

Is my data private?

Yes. Every calculation runs locally in your browser. Nothing you enter is uploaded, logged or stored.

Body fat vs. BMI — which is better?

Body fat percentage is generally more informative because it distinguishes fat from muscle, but it's harder to measure precisely. BMI is easier but blunter. Many people track both; you can compare with our BMI Calculator.

Sources

• Hodgdon, J.A. & Beckett, M.B. (1984). Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center.
• Deurenberg, P., Weststrate, J.A. & Seidell, J.C. (1991). Body mass index as a measure of body fatness: age- and sex-specific prediction formulas. British Journal of Nutrition.
• Jackson, A.S. & Pollock, M.L. (1978); Jackson, Pollock & Ward (1980). Generalized equations for predicting body density.
• American Council on Exercise (ACE) — body fat percentage categories.